Prediction of unsteady blade surface pressures on an advanced propeller at an angle of attack

This paper considers the numerical solution of the unsteady three-dimensional Euler equations to obtain the blade surface pressures of an advanced propeller at an angle of attack. The specific configuration considered is the SR7L propeller at cruise conditions with a 4.6-deg inflow angle corresponding to the + 2-deg nacelle tilt of the propeller test assessment flight test condition. The results indicate nearly sinusoidal response of the blade loading, with angle of attack. For the first time, detailed variations of the chordwise loading as a function of azimuthal angle are presented. It is observed that the blade is lightly loaded for part of the revolution and shocks appear from hub to about 80% radial station for the highly loaded portion of the revolution. DVANCED propeller tests in wind tunnels and in flight have been conducted to understand the aerodynamics and acoustics of advanced designs. Aerodynamic tests of the 9-ft-diam, single rotation SR7L NASA/Hamilton standard design were run in a transonic wind tunnel in Modane, France. Blade surface steady and unsteady pressures were measured during early 1987 on a two-blade configuration.1'3 (The com- plete eight-blade propeller was not tested due to drive power limitations.) The propfan test assessment (PTA) flight pro- gram (1987-1988) was managed by Lockheed Aeronautical Systems Company under a contract to the NASA Lewis Re- search Center. The 9-ft propfan was flight tested on a modi- fied, instrumented Gulfstream Gil business jet (Fig. 1). The objectives of the PTA program were to evaluate the propfan structural integrity, source noise, cabin noise, flyover noise, and enroute noise. Thus, an extensive data base has been established for the development and validation of propfan aerodynamic and acoustic analyses. In the PTA flight test program, the propfan propulsion system was mounted on the left wing of the modified Gil aircraft. This location was chosen to avoid flowfield interfer- ence with the main propulsion Gulfstream engines and to permit systematic investigation of the propfan characteristics.4 A nacelle tilt arrangement was employed to vary the inflow angle to the propfan. The variations in inflow conditions were used to evaluate the effects on cyclic stress of the propfan over a wide range of operating conditions. The inflow conditions also play an important role in the generation of noise. The three nacelle tilt angles of the test were - 3, - 1 (tilt down),